Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 130250
AFDLSX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
950 PM CDT Sat Apr 12 2014

.UPDATE:
Issued at 950 PM CDT Sat Apr 12 2014

Cold front located from near OMA extending southwestward into
central KS with a stationary front extending eastward from OMA
into central IA and near WI-IL border. Thunderstorms have
developed along both these fronts and are expected to largely
remain near them...well to our northwest...for a good part of the
night. Have adjusted PoPs to slow down timing into northeast MO
overnight.

Still expecting some development of SHRA/TSRA toward daybreak into
northeast-central MO. SHRA/TSRA then expected to maintain some
presence thru the day tomorrow on Sunday, increasing heading into
the afternoon. Convective development out ahead of the "main show"
over in eastern KS Sunday afternoon may interfere with its
strength and possible severe development.

TES

&&

.SHORT TERM:  (Through Late Tonight)
Issued at 338 PM CDT Sat Apr 12 2014

Warm front has surged northward with temperatures rising to
around 80 across the area. Gusty southerly winds will continue
overnight as the approaching cold front and low pressure area get
better organized. Thunderstorm development expected closer to the
front overnight from Kansas into Iowa...with most of the activity
expected in Iowa. Further south model soundings...especially GFS
which seemed to initialize the best this morning...show a cap
maintaining overnight. Storms may move into Northeast MO and West
Central IL by 12z...but development futher south will likely be
tough. Pops have generally been decreased overnight. Overnight min
temperatures also kept a bit above guidance given the wind staying
up overnight.

JPK

.LONG TERM:  (Sunday through Next Saturday)
Issued at 338 PM CDT Sat Apr 12 2014

(Sunday through Tuesday night)

Main concern continues to be the potential for a few severe
thunderstorms and locally heavy rainfall on Sunday afternoon and
Sunday night as the cold front moves southeast across the the area.
Not much change to the overall thinking of the forecast as
atmosphere will be fairly well capped most of the morning and
propagation vectors keep the expected MCS over IA, so showers and
storms chances should be stay confined to the the northern part of
the CWA during the morning hours.  By afternoon, a combination of
strong surface-850mb moisture convergence in conjuction with
increasing ascent with the mid level trough should be enough to
justify the categorical pops we already have going across central
and northeast Missouri/west central Illinois.  Kept near 100 percent
pops tomorrow night as low level convergence is strong underneath
the strong ascent of the trough.

Severe weather potential will mainly be during the late afternoon
and early evening hours along and ahead of the cold front over
central, east central and southeast Missouri as well as adjacent
sections of Illinois when convective inhibition erodes enough for
a few of the storms to become surface based. Deep layer shear
around 40kts will be sufficient for organized storms to produce
damaging winds and large hail. Precipitable water values are
around 1.4 inches, so the storms will be capable of producing of
heavy rainfall.

Did keep the likely pops for light rain a bit longer on Monday
morning as ascent from the upper trough does linger over CWA most of
the day per the GFS/ECMWF.  Also added a chance of light rain over
the eastern counties into Monday evening.   Upper trough will move
east of the area by 06Z Monday night, so kept Tuesday and Tuesday
night dry.

Kept the same temperature trends behind the front Sunday night into
Monday.  It still looks like temperatures by Tuesday morning will be
near or below freezing over much of the area after a weekend of well
above normal temperatures.

(Wednesday through next Saturday)

While both the GFS and ECMWF show a 500mb trough moving across the
central CONUS late mid-late next week, the GFS is much more
amplified with it than the ECMWF.  Consequently, it brings the
attendant cold front through the area slightly quicker on Friday,
and draws less moisture northward from the Gulf than the GFS would.
While the ECMWF does show some run-to-run continuity problems, the
GFS issues are slightly worse, so will favor the ECMWF with this
forecast.

Britt

&&

.AVIATION:  (For the 00z TAFs through 00z Sunday Evening)
Issued at 529 PM CDT Sat Apr 12 2014

Southerly winds will continue through the forecast period,
weakening a little tonight and losing some of the gustiness, but
becoming relatively strong and gusty again by late Sunday morning
well ahead of an approaching cold front. Models seem a little
bullish with pops tonight and am thinking most of the convection
will remain north and west of the taf sites, although may get
close to UIN and COU towards Sunday morning. Models also seem a
little overdone with development of MVFR cigs late tonight. For
now may keep it low end VFR in the warm sector, and include mainly
VCTS for UIN and COU Sunday morning and for the St Louis metro
area Sunday afternoon. May include prevailing showers/storms for
UIN and COU Sunday afternoon.

Specifics for KSTL: Sly winds should weaken some this evening and
lose some of the gustiness, then pick up again Sunday morning.
Mainly just high level clouds tonight, then low level VFR clouds on
Sunday with increasing low level moisture. Will go with VCTS
Sunday afternoon, then prevailing showers/storms Sunday evening
ahead of the approaching cold front.

GKS

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX






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